NASA’s Kepler mission confirmed the discovery of its first rocky planet, named Kepler-10b. Measuring 1.4 times the size of Earth, it is the smallest planet ever discovered outside our solar system.

The discovery of this so-called exoplanet is based on more than eight months of data collected by the spacecraft from May 2009 to early January 2010.

The Kepler mission is designed specifically to search for exoplanets roughly the size of Earth. It does this through a technique called the Transit Method.

Essentially, Kepler will watch a star for several hours. If a planet orbits that star, it may pass in front of the star and briefly reduce the apparent brightness. By measuring how much dimmer the star gets, and how often it happens, it is possible to determine the size and orbit period of the planet.

While this is a pretty cool discovery, don’t get your hope up about habitable planets yet.

Kepler is the first NASA mission capable of finding Earth-size planets in or near the habitable zone, the region in a planetary system where liquid water can exist on the planet’s surface. However, since it orbits once every 0.84 days, Kepler-10b is more than 20 times closer to its star than Mercury is to our sun and not in the habitable zone.